The net torque produced by an engine, for example, an Otto or a Diesel internal combustion engine, is the total or gross torque produced by the engine, less the sum of internal and external torque losses. Internal losses are dominated by friction between the relatively moving parts of the engine. External losses may be those caused by accessories driven by the engine, such as an alternator, air conditioning unit, power steering unit, and also any torque converter losses from an automatic transmission.
It is desirable to be able to predict the net torque expected from an engine as a function of the driver demand from the accelerator pedal and gearbox setting. For example, an electronic power train control module in a motor car may control a fuel pump and fuel injectors, depending on the driver demand. An estimated net torque is useful, for example, in the control of automatic transmission and drive wheel traction control, so that gear shifts occur at the right time, and the drive wheels maintain friction with the road.
While in principle it is possible to measure and model accurately the expected net torque produced by an engine operating in a steady state condition, in practice different engines of the same type will have slightly different characteristics, and these characteristics will vary depending on a number of factors such as engine age and operation history. Other factors, for example, engine operating parameters that are not normally measured, such as barometric pressure, relative humidity, and ambient temperature, may have an appreciable effect on the engine net torque.
A number of systems have therefore been proposed to measure or estimate the engine net torque. Most of these, however, involve a continuous adjustment of stored parameters used in torque loss calculations, at least during steady state operation of the engine. This modeling approach involves relatively complex circuitry and software in order to achieve an accurate result.
Another system, disclosed in U.S. Pat. No. 5,484,351, uses an adaptive memory to update stored parameters, but only when the engine is in idle, with no driver demand from an accelerator pedal. When a driver demand is present, no calculation is performed to adjust torque values, and it is possible that the torque correction values for the idle condition would not be correct when driver demand is present and engine speed is generally higher. Another feature of this prior art system is that the torque correction is an adjustment to the driver demand signal, and therefore cannot be used as a net torque estimate to achieve better control of drive train components such as a traction control module or an automatic transmission.
It is an object of the present invention to provide a more convenient apparatus and method for estimating the net engine torque, which does not rely on continuous or frequent adjustment of stored parameters used in torque loss calculations.